With advances in integrated circuit, microprocessor, networking and communication technologies, an increasing number of devices, in particular, digital computing devices, are being networked together. Such devices are often first coupled to a local area network, such as an Ethernet-based office/home network. In turn, the local area networks are interconnected together through wide area networks, such as Synchronous Optical Networks (SONET), Asynchronous Transfer Mode (ATM) networks, Frame Relays, and the like. Of particular importance is the TCP/IP based global internetwork, the Internet. The rapid growth of the Internet has fueled a convergence of data communication (datacom) and telecommunication (telecom) protocols and requirements. It is increasingly important that data traffic be carried efficiently across local, regional and wide area networks.
The widespread deployment of high-speed networking and communications equipment has produced a large demand for various types of networking and communications components and subsystems. Included among these, are modules, which are often referred to as optical transponders.
Optical transponders typically include components for both electrical signal processing, and components for transmission and reception of optical signals. Conventional optical transponders typically receive data representing electrical signals in parallel, serialize the data represented, encode the serialized data onto a light-based signal, and couple that optical signal to an outbound optical fiber. Similarly, conventional optical transponders, typically receive a light-based signal having data serially encoded thereon, recover the data in an electrical form, de-serialize the data and provide them in a parallel format to a plurality of output terminals.
Conventional optical transponders typically include a case, or housing, within which the electrical and optical components are enclosed. Such a housing provides physical protection for the components therein, and also provides thermal conductivity so that heat may be dissipated from the components disposed within the case. The number of components may be numerous. However, a requirement of the housing is that the housing be of a small form factor. Accordingly, in order to have the components within a housing of a small form factor, placement of the components is an important aspect of the optical transponder.
Placement of the components may be determined by one component's operation relative to another's. For example, as described above, a component, such as a semiconductor light source, that operates to provide light-based signals is placed in such a manner as to be optically coupled to another component, such as an optical fiber, that operates to optically transmit light-based signals.
Integrity of the light-based signals and stability of the semiconductor may be based upon power output of the semiconductor light source. Accordingly, an important component of an optical transponder is semiconductor light source monitoring device, such as a photodetector, that can monitor the power output of the semiconductor light source. Due to design of a common semiconductor light source used in optical transponders, the semiconductor light source can provide light in more than one path, e.g., two light paths, simultaneously. One light path, commonly known as light source facet, is directed to the optical fiber. Another light path, commonly referred to as back facet, may be directed to a light receiving area of the photodetector. The photodetector receives the light via the light receiving area, or window, and the light is converted to electrical signals, which are sent to another component to be processed to determine the integrity of the light-based signals and stability of the semiconductor light source (i.e., optical power, temperature, and the like). This monitoring is commonly referred to as back-facet monitoring (BFM). The light source facet and the back facet are on opposite sides of each other. Accordingly, placement of the photodetector is opposite side of the semiconductor light source coupled to the optical fiber.
As the form factor of the housing of the optical transponder continues to become smaller, placement of the photodetector in the light path opposite the optical fiber side of the semiconductor light source becomes increasingly difficult due to various components included in the housing.